Intercarrier-video type television receiver



Patented Apr. 7, 1953 INTERCARRIER-VIDEO TYPE TELEVISION RECEIVER l Carlton E. Bessey,l North Long Branch, N. J. E Application January 21, 1949, Serial No. 71,848

11 Claims.

i This invention relates to radio receivers; in

particular, it concerns an improved and simpli- `fied system for receiving the sound and picture signals transmitted by standard television broadcasting stations.

A television signal, as transmitted from a 4broadcast station, is extremely complex. A television station is normally assigned a channel `in the frequency spectrum having a total width of 6 megacycles; that is, for example, a particular station might be assigned a channel ex- `tending'from 54 to 60 megacycles. Two carrier signals are transmitted within that spectrum by the transmitting station; these are respectively the sound carrier and the picture carrier. The sound carrier usually is on a frequency` 0.25 megacycle lower than the upper edge of the assigned channel; in the'example given, the sound carrier would be at 59.75 megacycles. The picture carrier is normally on a frequency 4.5 megacyeles lower than the sound carrier; in the example given, therefore, the picture carrier would be on 55.25 megacycle-s.

Frequency modulation is applied to the sound carrier for the transmission of the voice program normally accompanying a television picture. Amplitude modulation is employed on the Vpicture carrier to transmit the video impulses which, at the receiver, are usedto paint the picture on a cathode-ray tube. The spectrum of the FM sound signal is normally 200 vto 300 kilocycles Wide, 100 top150 kilocycles on each `side of the sound carrier, I and it .is thus con- -nedfwithin theupperedge of the assigned '.channel. The side-band components produced -by amplitude."modulation of the picture carrier extend, in theory, from a few cycles per second to about 4 rnegacycles per second. As a prac- -tical matter, very low frequency video components are of no practical importance, and the significant range of video frequencies is from about one hundred cycles per second to about 4 megacycles per second. Amplitude modulation vnormally produces side-bands distributed symmetrically on either side of the carrier frequen- Acy. In television practice, in orderto prevent excessive channel width, the lower video sideband is partially suppressed at the transmitter. so that no signals of appreciable amplitude are transmitted on frequencies lower than the lower edge of the assigned channel. The upper sideband is transmitted fully, without suppression.

Conventional television receivers employ the -superheterodyne circuit; a radio-frequency am- .,plier andmixer circuit is provided having a pass-band which can accommodate theentire frequency range occupied by vthe transmitted television signal. The signalfrom alocal oscillator within the receiver is mixedwith thevtelevision signal, and the resulting' difference frequencies are amplified in separate I. F. amplifiers. The 'sound I. F. amplifier is designed to have relatively sharp response, so that it accepts and amplifles the sound carrier withiits FM side-band components but rejects the video signals. The video I. F. amplifier is designedto have wide-band characteristics so as to amplify .the video signal; so far as practicable, the lim'- its of its pass band are chosen to rejectthe sound signal. The major practical diiiiculty in the present day television receiver lies in the local oscillator. Frequency stability in that oscillator is of, the very greatest importance. If the oscillator drifts after the receiver has once been tuned to a particular station, both the sound andthe picture will be adversely affected. The sound I. F. channel is quite narrow, and accordingly only a small frequency drift by the local oscillator is necessary to de-tune the sound channel completely or to such an extent that quality of reproduction is badly impaired. Local oscillator drift affects the picture by causing the I. F. amplifier to reject a portion of the video spectrum or, if the drift is in the direction which brings the sound carrier into theV pass band of the picture I. F. amplifier, the presence of the unwanted sound carrier in the 4video signal spoils the picture by cross-hatchingit with black lines or other spurious .markings on the screen of the picture tube. Engineers have long been well aware that local oscillator drift should be avoided, but no practical means of preventing it in an inexpensive receiver has existed. Crystal control for the local oscillator is the best solution, but it is prohibitively expensive for all except the highest priced receivers. Various systems of automatic frequency control have been suggested, but they are expensive and their reliability has not been good. The frequency of the local oscillator is necessarily of the same order of magnitude as the television carrier frequenciesthat is, local oscillator frequency will normally range between approximately 40 and 250 megacycles per second, according to the particular television channel being tuned in. Even though great care may be employed in the design of the circuit and the choice of components, it is extremely diiiicult and expensive to 4designa By eliminating that component,

have ended the problem of receiver drift and have accomplished good reception of television signals with a much simpler circuit than has heretofore been required.

Accordingly, one of the major objects of this invention is to provide a television receiver, having the benefits of the s uperhcterodyne circuit', which has no local oscillator.

"Another object of my invention is to provide -a television receiver wherein the. receiver drift Vcharacteri'stic of prioreart receivers has been on. tirely eliminated.

further object of my invention 'is toy provide a television receiver employing fewer components and-a more simple circuit than has` been previously required to accomplish similar results.

A still 'further object of my invention is to 'providea television receiver inwhich the sound 4carrieris suitably amplied and iilteredV and thereupon `mixed :with the. picture carrier and -thevi'deosideeband components to provideian LF: signal for amplificationpby the; picture i. F. ampliiier. Still another object of my Vinvention is to provide'a television receiver wherein the sound receptionis accomplished by a simple circuit while vv.reception of video signals is accomplished by a superheterodyne circuit employing the sound calllrierjsuitably ampliiied and ltered, in` lieu of a .locali oscillator.

Other objects andadvantagesof my invention -vvillappear asthespecication proceeds. "Ihaveillustrated one illustrative embodiment 'of my invention` in the accompanying drawing, vof whichligurel is a schematic andv diagrammatic showing .of a television receiver made according-to my invention; and Fig.. 2 is a graph showing the frequency-response characteristics "offa typicalLrI'. F. amplifier designed in accordance with my invention.

is shown in Fig. l, signals are interceptedon 1anA antenna Ill, which. maybe a broad-:band dipole .op other suitableentenna. A transmission line II couples the antenna to an, input coil i2 which is; in: turn, inductively coupled to coils Iiand t4. The inductive coupling between coils i2 and I3; should be relatively close, while the coupling betweenvcoil l2 and coll it. should be very loose.

Coil; I4l is shunted by a condenser l5, which may be variable, to form a tank circuit. One sideof condenser [51 is` grounded; the other ter- 'minal is connected to the control grid of tube 2li, which. functions as a radio-frequency ampliner for the soundv signals. Tank circuit Ii,l I5 is a high-Q circuit, and its :resonant frequency is set to that of the sound carrier.

The, suppressor .gridand cathode of tube 2t fare..connectedtogether, and they are connected tto ground. thro11gh RIF. by-pass condenser I6. Condenser Ii-` is shunted by vcathodebiasing re- .fsistor I The screenl grid or" tube 2 51 is connected to the positive side of D.C. voltage source |08 through de-coupling resistor I8. side of voltage source I is grounded. The screen grid of tube 2e is by-passed to ground by condenser I9.

The plate load circuit of tube 26 comprises a high-Q tank circuit made up of coil 2| and condenser 22, which may be variable. One terminal of tank circuit 2l, 22' isA connected to the positive side of voltage source me.' The plate of tube 2G is connected to a tap on coil 2l near the end connected to voltage source |852. A Icy-pass condenser 23 is connected between the positive side or" voltage source IBB and ground.

The other side of tank circuit 2|, 22 is connected through grid coupling condenser 23 to the control grid Vof tube 3). The control grid is also connected through resistor 2li with the AVC circuit which will be hereinafter described.

The suppressor grid of tube 30 is connected to the ,cathode and; they are' connected to ground through R. F. Icy-.pass condenser 2%. .Condenser 25 is shunted by cathode-biasing'resistor 26,; The screen grid of tube t, is connected to the. pcsie tive side of voltage source it@ through dii-@Qui-L pling resistor 2i; and the screen grid of tube) is Icy-passed toground through condenser 2S.4` `A very-high-Q tank circuit is formed by' coilv 29 and condenser 3E, whichmay be variable. One side of .that tank*circuit is connected-to the positive side of voltage.- source I; its other side is connected through `coupling condenser 32;:to the-control grid of tubey zich.. The platey of tube 30 is connected to a tap-on-coi-l 29nearthe end thereofV whiclris'connected to voltage source itil'.

As will be hereinafterz'rnorefully` described under opePatio-nf"v tank circuit-'21,` 22'is tuned to a frequency a few hundred kilocycles higher or lower than Athat of' thev sound carrier; while tank circuit 29; 3l is normally tuned squarely to the ksound carrier, although, aswill. be herein,- after more ful-ly described'. it may .ony occasion be tuned somewhatv otthe. sound' carrier on the other side of the sound carrier from tankci'rcuit ZI., 22;.Y i

The. junction ofYY condensers 23 and22 is connected through coupling condenser 33, to the control grid` of tube 5l). Grid resistor- 34 is connected betweenythe control grid of. tube 50' and ground'. The suppressor grid and cathode of tube 50 areV connected together and grounded. Resistor 3,5 connects. the-junctionof condensers 'gand; 23 to the. screengrid o tube, 50, and a variable resistor 3.6 is connected between/the Screen grid. Qf tube 50 and ground., The plateof tube' 50; is connected through load resistor 31 to the positive side of voltageV sourceY 100, and a coupling condenser 38 connects .the plate of tube 513 to the'input of an audio-frequency amplifier 39' which, being conventional, is shown diagrammatically in Fig. l. Amplifier 39 is connected to a conventional speaker 4I.V

Coil IBfisshunted by acondenser '42! to form 'a tank circuit, and it is also shunted by a loadnected to ground throughvR; F; by-'pass-condenser 44.- Condenser 44 isA shunted by cathode:- biasing. resistor 45. The screen grid oftubi The negative is connected through de-coupling resistor 46 to the positive terminal of voltage source |88, and the screen grid of tube 60 is connected to ground through by-pass condenser 41. The plate load circuit of tube 50 comprises a radio-frequency choke coil 48 .and a load resistor 49, connected in series. One end of resistor 49 is connected to the positive side of voltage source |88, while the open end of choke coil 48 is connected to the plate of tube 60.

` The plate of tube 60 is connected through coupling condenser 5| to the control grid of tube 40a. The control grid of tube 40a is connected to ground through grid resistor 52.

. Tubes 48a and 48h are triodes which may, if desired, be mounted within a single envelope as indicated on the drawing. y The cathodes of tubes 40a and 48h areconnected together and grounded. The plates of tubes 49a and 40h are connected together and areconnected to one side of the tank circuit comprising condenser 53 and coil 54. The other side of tank circuit 53, 54 is connected to the positive side of voltage source |80 and is also connected to ground through by-pass condenser 55. Condenser 53 and coil 54 may each be variable as shown in the drawing. Tank circuit 53, 54 is shunted by a loading resistor 58 which mav be so chosen as to reduce the effective Q of the circuit to unity. In a typical embodiment of my invention, tank circuit 53, 54 may be tuned to resonate at 3.5 megacycles, as indicated on the drawing.

Thecontrol grid to tube 48h is connected to ground through resistor 32a.

The plates of tubes 48a and 48h are connected through coupling condenser 51 to the control grid of tube 18. The control grid of tube 18 is connected to ground through resistor 58. The suppressor grid of tube is connected to its cathode, and they are connected to ground through by-pass condenser 59. Condenser 59 is shunted by cathode-biasing resistor 8|. The screen grid of tube 10 is connected to ground through by-pass condenser 82. and is connected through de-coupling resistor 63 to the positive side of voltage source |88. The plate of tube 18 is connected to one side of a tank circuit comprising condenser 84 and coil 65. The other side of tank circuit 54. 55 is connected to the screen grid of tube 18. A loading resistor 88 is shunted across tankcircuit 64, v55S to reduce its effective Q to a value of about 2. The coil 55 may be a variable inductance as shown in the drawing. and condenser 64 may, if desired, be made variable. In the typical embodiment illustrated. the resonant frequency of tank circuit 54, 65 should be 0.5 megacycle.

'I'he plate of tube 18 is connected through coupling condenser 51 to the control grid of tube l8|), and that control grid is connected through resistor 68 to the AVC circuit to be described hereinafter. The cathode and suppressor grid .of .tube 80 are connected together, and are grounded through by-pass condenser 59. Convdenser 89 is shunted by cathode-biasing resistor 1|. The screen grid of tube 88 is connected to ground through by-pass condenser 12 and to the high voltage side of voltage source |88 through decoupling resistor 13. The plate of tube 80 is connected to Yone side of a tank circuit comprising condenser 14 and coil 15. Either or both of vthese elements may be variable, as shown in the drawing. The other side of tank circuit 14, 15 is connected to the screen grid of tube` .88. Tank circuit 14, 15 is shunted by loading resistor 16, which maybe chosen to have a value such" that the effective Q of tank circuit 14, 15 is about 2, and in the typical embodiment shown the resonant frequency of tank circuit 14, 15 should be 3.5 megacycles.

The plate of tube 89 is connected through` coupling condenser 11 to the control' grid of tube 98, and the control grid of tube is connected to ground through grid resistor 11a.v

The suppressor grid and cathode of tube 90 are connected together and are grounded through by-pass condenser 18. Condenser 18 is shunted Aby cathode-biasing resistor 19. The screen grid of tube 90 is connected to ground through by-pass condenser 8| and is connected to thepositive side of voltage source |08. through de-v unity. In the typical embodiment shown, the` resonant frequency of tank circuit 83, 84 should beV 0.55 megacycle.

The plate of tube 98 is connected through cou` pling condenser 86 to the plate of diode detector tube H8. The cathode of diode ||0 is grounded. A low-pass lter consisting of choke coils 81 and 88 in series is connected between the plate of diode ||8 and one terminal of detector load re The other terminal of load resistor 9| sistor 9|. is grounded. A condenser 89, forming part of the low-pass lter, is connected between ground and the junction of coils 81 and 88. Y

The ungrounded side of load resistor 9| is connected to the input of a video amplifier 99, with associated sweep and synchronizing circuits for the cathode-ray tube 98 driven by the video amalifier. Since these last-mentioned elements are '.onventional, they areshown diagrammaticallyl on Fig. 1.

The AVC circuit, which has been referred to, is operated from the intensity grid of the cathode-ray tube. As shown in Fig. l, a coupling condenser 92 is connected between the intensity grid of the cathode-ray tube 98 and the plate of diode |28. The cathode of diode |28 is ground ed. A high resistance 93, which may be of several megohms value, is shunted between the plate and cathode of diode |28. A low-pass filter comprising resistor 94 and'condenser 95 is connected between the plate of diode |28 and ground, and a potentiometer 96 is shunted across condenser 95. The resistance of both element 84 and potentiometer 95 should be of high ohrnic value. The variable tap on potentiometer 96 is connected to the control grid of tube 30 through resistor 24 and to the control grid of tube 80 through resistor 88.

Operation Before taking up the operation in detail, I shall review briefly the functions of the various tubesin the circuit shown in Fig. l. Tube 59 is a radio-frequency amplifier adjusted to give maximum and substantially equal response to the picture carrier and its associated side-band components. Tube 20, on the other hand, is a radio-frequency amplifier having a high-Q tuned grid circuit and adjusted to respond to the sound carrier and its side-band components'. Tube 39 is a high-gain ampliiier tube associated with a sharp .band-nass: dlter which. has. the functionV oframplifyingthe sound carrier and discriminate. ine, against. its associated solefband c oirinonents.v 'lubei 58:15; the sound detector; tube, operating as a regenerative amplifier andempleying slope de -V tection to; derive anv aud-io; envelope from.` the frequency-modulated signal: fed to, its input.

Y'luloes 49e and-4Gb collectively form a non linear 'mixers circu it the function of whichk is. to. combine` the: pictureV carrier and its sideband components with; the sound carrier after it'has; been amplified and stripped of its sideband components.- Tubes lll, 8,0, and l) comprise a stagser-tunedl. F. amplifier designed. to sive substantially'. flat rmnonse over the baud between. 0.5.y mesacycle and; 4. meeacycles. to discriminate sharply against. frequencies; lower than,(l.5megaeycle, and to drop at the high. frequency end at; such a rate that the response at 4.5, megacycles is 6 db below the average respense'. Tubel l Ill is; a conventional diode detector tube; similarly tube lil! is a conventional dioderectieri having the function of reetifying the Videosignal; voltage to supply control voltage. for AVC purposes.A

I shall now review the operation of, my receiving system in somewhat more detail. TheV amplifier tube 2li operates with its grid circuit tuned to the sound, carrier; the pass band oftank circuit I4, l5, While sharp enough to suppress the video signals, will pass the sound carrier and the FM side-band components readily. Tank circuit 2l, 22', which is loosely coupled tothe plateV of tube 20, isV a high-Q circuit which is adjusted for slope detection-that is, its resonant frequency is set to a frequency removed from the soundl carrier by perhaps 260 kilocycles. The frequency modulation of the sound carrier causes a diiferential resp-onse in tank circuit 2l, 2-2, the developed` Voltage being greater when the frequency swings toward the resonance peak and less when the frequency swings awayV from the resonance peak. This results in changes in the average grid voltage of tube Ell which correspond to the audio envelope of the voice signal being transmitted, and those audio voltage variations produce corresponding changes in the plate current of Vtube 5G. As a result, an audio voltage is developed across plate load resistor 3l and is fed to and amplified by amplifier 39'.

The voltage across tank circuit Zi, 23 is also applied to the control grid of tube 3S; The plate circuit of tube 30, however, is connected to a `very sharp, high-Q circuit which is preferably tuned to the exact frequency of the sound carrier. In 4certain cases, it may be desirable, in order to maintain tube Silin a conditionY of complete stability, to have circuit 29, 3l tuned off the soundcarrier in the opposite direction from the deviation of tank circuit 2l, 22. If this is done,` however, a supplemental band-pass filter, which may consist of one or more sharplytuned circuits and, if desired, another coupling tube, should be connected between the output of tanky circuit 29, 3l and the grid of tube dub. The object of tank circuit 29, 3l, or of an additional, supplemental band-pass filter, if one be used, is to attenuate the FM side-band components which are initially received from the tele-f vision transmitting station and to obtain an amplified signal which is predominantly the sound carrier.

Complete suppression of the FM side=band components is, of course, not practicable except by, the usel of a. very elaborate circuit. I have 8: found, however., that complete. suppression of. the side-band components, is noty necessary; it, is sulicient ifA they arel attenuated relative to thel sound carrier so` that the strongest of them remains at a power level of the order of 1Q to.

12 db belowv the soundl carrier level,

Theampltude of they sound carrier, as applied tot the grid of tubel 4Gb,- Will normally be several. volts, AsY a result, it. accomplishes ecieutly conversion of the picture signal applied to thev grid. of tube @0a from its original carrier fre-V quency toa new carrier frequency equal to the diference between. the transmitted picture oar-f rier and the sound carrier., IIhis differencel is. normally 4.5 meeacycles.. andthe Signal fed into the input.- of.' tank circuit 5,3, 5.4, thus consists ot the carrier of 4.5 mesacucles, the complete side-band4 ranging from 4.5 megacycles downto a. few hundred kilocycles, and the residual side-.. band which ranges from 4.5 megacycles to about 5.75. megacycles.

Amplication of the residual side-band is not. necessary; in fact, it isl desirable that it be attenuated relative to the major side-band.. Age cordingly, the I. F. amplifier following. the; mixercircuit should respond readily to and amplify equally frequencies between about 0.5. megacycles and 4. megacyclesand should cut off. fairlyrapidly outside that band. The: I. F. amplifier shown in F'ig. l accomplishes. that result and pro-,- vides an over-all gain of about, 60 db- Fig. 2 shows the response of that amplifier, plotted with gain inV decibels. as the dependent variable and with frequency in megaoycles per second as the` in dependent variable.

From an examination .of Fig. 2 it will be seen that a typical amplifier is flat Within about 2 dbr for all frequencies. between 0.5 megacycle and 3.8 megacycles; and the response at 4 megacycles is down only about 3 db from the maximum.

The low-pass filter associated with diode de. tector tube HB is. eifective to suppress from the detected videosignal any frequency components on the high lside of 4.5. megacycles which remain after the signal has passed through the video amplier, and accordingly the video` signalfed to amplier t9 faithfully reproduces the video envelope transmitted by the television station.

VThe AVC voltage may be obtained by any convenient means; in the illustrated embodiment I chose. torectify the video -signal voltage on the grid of the picture-tube. By appropriate setting of potentiometer 85, a satisfactory automatic Volume control-of both the sound and the picture sectionsiof` the receiver can be obtained.

I have, asa-matter of conveniencel and for the purpose of keeping the Schematic diagram clear-f ly readable, shown the various signal-.frequency circuits as being independently tunable. In practical embodiments of my invention it4 will normally be desirable to provide several different circuits, pre-tuned for thev television channelsv to be received, with one of the Well-known ,switching methods. employedfor cutting in theV setl of circuits desired. for reception of a particular tele-v Vision station. j

While I havev inY this specification described K in considerable detail aparticular embodiment o f my invention for illustrative purposes, it will be understood that those skilled in the art can make a large number of changes in details with out departing from the. spirit and basic. principles of my invention. Aocordinglnthe. Scope of; invention is not. to be. considered as limited to the particular arrangement of components. shown 9e in the drawing, but is to be determined by reference to the appended claims.

I claim:

1. In a receiver adapted to receive a television signal comprising sound and picture carriers separated in frequency by a predetermined interval, said sound carrier having associated with it sidebands carrying sound intelligence and said picture carrier having associated with it side-bands carrying video intelligence, a first tunable input circuit normally tuned to the frequency of the sound carrier, an amplifier coupled to said input circuit, a tunable filter connected in circuit With said amplifier normally tuned to pass signals of the sound carrier frequency and to attenuate relatively thereto signals of other frequencies, a second tunable input circuit normally tuned to said picture carrier and its side-bands, a mixer circuit comprising an element having a nonlinear voltage-current characteristic adapted to combine a signal of the sound carrier frequency derived from said amplifier and filter with the picture carrier and its side-bands, and circuit means coupling the filter and the second input circuit to said mixer.

2. In a receiver adapted to receive a television signal comprising sound and picture carriers separated in frequency by a predetermined interval, said sound carrier having associated with it sidebands carrying soundintelligence and said picture carrier having associated with it side-bands carrying video intelligence, a first tunable input circuit normally tuned to the frequency of the sound carrier, an amplifier coupled to said input circuit, a tunable filter connected `in circuit with said amplifier normally tuned to pass signals of the sound carrier frequency and to attenuate relativelyl thereto signals of other frequencies, a second tunable input circuit normally tuned to said picture carrier and its sidebands, a mixer circuit comprising an element having a nonlinear voltage-current characteristic adapted to combine a signal of the sound carrier frequency derived from said amplifier and filter with the picture carrier and its side-bands, circuit means coupling the filter and the second input circuit to said mixer, and an I. F. amplifier fed by the mixer circuit adapted to amplify selectively-the difference-frequency signals generated therein.

3. In a receiver for reception of television signals comprising a -sound carrier and a picture carrier differing in frequency by a predetermined amount, each of said carriers having side-bands associated therewith, a coil adapted for connection to an antenna, a first tunable input circuit coupled to said antenna coil and normally tuned to the frequency of the sound carrier, an amplifier coupled to said first input circuit, a tunable filter connected in circuit with said amplifier normally tuned to pass signals of the sound carrier frequency and to attenuate relatively thereto signals of other frequencies, a second input circuit coupled to said antenna coil normally tuned to respond selectively to the picture carrier and its side-bands, and mixer means comprising an element having a non-linear voltage-current characteristic and provided with two input channels, one of said input channels being fed with signals derived from said second input circuit and the other of said input channels being fed by signals derived from said amplifier and filter.

4. In a receiver for reception of television signals comprising a sound carrier and a picture carrier differing in frequency by a predetermined amount, each of said carriers having side-bands associated therewith, an antenna coil, a rst input circuit coupled to said antenna coil and normally tuned to the frequency of the sound carrier, an amplifier coupled tosaid first input circuit, a lter connected in circuit with said amplifier normally tuned to pass signals of the sound carrier frequency and to attenuate relatively thereto signals of other frequencies, a second input circuit coupled to said antenna coil normally tuned to respond selectively to the picture carrier and its side-bands, mixer means comprising an element having a non-linear voltage-current characteristic and provided with two input chambers, one of said input channels being fed with signals derived from said second input circuit and the other of said input channels being fed by signals derived from said amplifier and filter, and an I. F. amplifier fed by said mixer means and responsive selectively to the difference-frequency signals generated in said mixer means. l

5. In a receiver adapted to receive a television signal comprising sound and picture carriers separated in frequency by a predetermined interval, said sound carrier having associated with it sidebands carrying sound intelligence and said picture carrier having associated with it side-bands carrying video intelligence, a iirst tunable input circuit normally tuned to the frequency of the sound carrier, an amplifier coupled to said input circuit, a nlter connected in circuit with said am.- plier normally tuned to pass signals of the sound carrier frequency and to attenuate relatively thereto signals of other frequencies, a sec'.- ond input circuit responsive to said picture carrier and its side-bands, a mixer circuit comprising an element having a non-linear voltage-current characteristic adapted to combine a signal of the sound carrier frequency derived from said arnplifier and filter with the picture carrier and its side-bands, circuit means coupling the filter and the second input circuit to said mixer, and detector means coupled to said first input circuit op: erative to derive audio-frequency signals from said sound carrier and its side-bands.

6. In a receiver for reception of television sig.- nals comprising a sound carrier and a picture car',- rier differing in frequency by a predetermined amount, each of said carriers having side-bands associated therewith, an antenna coil; a first input circuit loosely coupled to said antenna coil and normally tuned to the frequency of the sound carrier, an amplifier` coupled to said first input circuit, a lter connected in circuit with said amplier normally tuned to pass signals of the sound carrier frequency 'and to attenuate relatively thereto signals of other frequencies, a second input circuit tightly coupled to said antenna coil normally tuned to respond selectively to the picture carrier and its side-bands, and mixer means comprising an element having a non-linear voltage-current characteristic and provided with two input channels, one of said input channels being fed With signals derived from said second input circuit and the other of said input channels being fed by signals derived from said amplifier and filter.

7. A receiver for reception of television signals comprising a sound carrier and a picture carrier differing in frequency by a predetermined amount, each of said carriers having side-bands associated therewith, comprising a first input circuit selectively responsive to the sound carrier, a second input circuit selectively responsive to the picture carrier and its side-bands, a high-Q resonant filter coupled to the rst input circuit operative to attenuate the side-bands of the sound car.-`

rier relative to said sound carrier, mixer means for mixing the sound carrier as iiltered with the picture carrier and itsy side-bands, and circuit means'for feeding the picture carrier and its sidebandsand said ltered sound carrier to said mixer means.4

8.V A receiver for reception of television signals comprising a sound carrier and a picture carrier differing in frequency by a predetermined amount, each of said carriers having side-bands associated therewith, comprising a first input circuit selectively" responsive to the sound carrier, a second input circuit selectively responsive to the picture carrier and its side-bands, a high-Q resonant filter operative to attenuate the side-bands of the sound carrier relative to said sound carrier, means for mixing the sound carrier'as filtered with the picture carrier and its side-bands, cir'- cuit means forv feedingsaid filtered sound carrier and said picture carrier and its side-bands to said mixer means, and an I. F. amplifier fed by the mixer means selectively responsive to the diierence-frequency components of signal developed in said mixing means.

' 9. A receiver for reception of television signals comprising a sound carrier and a picture carrier differing in frequency by a predetermined amount, each of` said carriers having side-bands associated therewith, comprising an input circuit selectively responsive to the sound carrier and its side-bands, a second input circuit selectively responsive to the picture carrier and its side-bands, detector means coupled to the input circuitv opera'- tive toderive audio-frequency signals from said sound' carrier and its sidebands, resonant iilter means coupled to said input circuit operative to attenuate the side-bands of the sound carrier relative to said sound carrier, and means for mixing the sound carrier as ltered with the picture carrier and its side-bands.

10. A television receiver for. reception of television signals comprising a sound carrierV and a picture carrier diiering Vin frequency by a predetermined amount, each of said carriers having side-bands associated therewith, comprising an input circuit selectively responsiveto 'the sound carrier and its side-bands, a second input circuit selectively responsive to the picture carrier and its side-bands, detector meanscoupled to tneinput circuit operative to derive audio-frequency signals from said sound carrier and its side-bands, high-Q resonant lter means coupled to theinputcircuit operative to attenuate '-theY-side-bands of the sound carrier relative to said sound carrier, means for mixing the soundv carrier as filtered with the picture carrier and its side-bands, circuit means for feeding said filtered sound carrier and said picture carrier and side-bands to" said mixer means, and an 1. F. amplifier fed by said mixer means responsive selectively to the difference-frequency components of signal developed in said mixing means.

11. In a television receiver forreception-of televisionv signals comprising a'sound carrier and a picture carrier; diifering in frequency by a pre# determined amount, each of said carriers having side-bands associated therewith,l a tuned input circuit normally tuned to respondselectivelyto the sound carrier frequency, an amplifier coupled to said input circuit,`a tuned input circuity normally tuned to respond selectively tothe picture carrier and its side-bands, mixer means `fed by the amplier andthe second input circuit, and an I. F. amplier fed by the. mixer and responsive selectively to the diiierence-f-requency signals generated in said mixer, comprising an I. F; carrier equal in frequency to the difference between the carrier frequencies, and side-band components derived from the side-'bands of the picture car rler.

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